Method and apparatus for post tensioning and anchoring prestressing tendons

ABSTRACT

A method and apparatus for post tensioning a prestressing tendon disposed in a concrete structure through the employment of a first jack to impart a uniform predetermined tension to the tendon, and a second jack used in conjunction with an engageable anchor to selectively engage the anchor to the prestressing tendon and place he anchor in abutment with the concrete structure. The jacks are separate and separable from each other to facilitate preassembly of the second jack nd anchor on a tendon prior to the application of the first jack.

United States Patent Inventor Lawrence R. Yegge 139 Via de Tesoros, LosGatos, Calif. 95030 Appl. No. 780,111

Filed Nov. 29, 1968 Patented Aug. 10, 1971 METHOD AND APPARATUS FOR POSTTENSIONING AND ANCHORING PRESTRESSING TENDONS 10 Claims, 4 Drawing Figs.

US. Cl 29/452, 254/29 A Int. Cl 321d 39/00, 1321b 19/00 Field of Search254/29 A; 29/452; 52/223, 225, 230

[56] References Cited UNITED STATES PATENTS 3,338,552 8/1967 Persicke254/29 3,338,553 8/1967 Persicke 254/29 3,412,511 11/1968 Dietrich254/29 X 3,491,143 1/1970 Pewitt 29/452 Primary Examiner-R0bert C.Riordon Assistant ExaminerDavid R. Melton Attorney-Naylor & NealABSTRACT: A method and apparatus for post tensioning a prestressingtendon disposed in a concrete structure through the employment of afirst jack to impart a uniform predetermined tension to the tendon, anda second jack used in con- 7 junction with an engageable anchor toselectively engage the anchor to the prestressing tendon and place heanchor in abutment with the concrete structure. The jacks are separateand separable from each other to facilitate preassembly of the secondjack nd anchor on a tendon prior to the application of the first jack.

Patented Aug. 10, 1971 V 2 Sheets-Sheet 3 INVENTOR. LAWRENCE l3. V6665 IATTORNEYS METHOD AND APPARATUS FOR PosT T'ENSIONING AND ANCHORINGPRESTRESSING TENDONS BACKGROUND OF THE INVENTION The present inventionrelates to posttensioning a concrete structure, and specifically to amethod and apparatus for applying a uniform tension to and anchoring aprestressing steel tendon. The invention is also concerned withuniformly tensioning and anchoring each strand of a multiple-strandprestressing tendon to the concrete structure within which it has beenincorporated.

Posttensioning is a method of prestressing concrete with which thepresent invention is concerned. This is the method of stressing thesteel tendon members after the concrete has been formed and cured, andcausing that stress to be borne uniformly throughout the length of thecomposite concrete and steel structure. To accomplish a uniform stressdistribution, it has been found necessary to apply an initial tension tothe tendon in excess of the working stress desired in order to overcomethe effects of friction between the tendon and the concrete. The tensionis then reduced to a predetermined value to obtain a uniformdistribution of stress'along the ten-' don.

In posttensioning methods, the tendon is held under this 7 uniformtension while it is anchored to the concrete in order that the prestressbe retained in the composite structure when the externally appliedtension is released. One means of accomplishing this anchorage, which isconveniently effected at the site of construction, is through the use ofcollar-shaped wedges in conjunction with a conical receiving hole, asshown in the prior art and illustrated in U.S. Pat. No. 3,090,598. Thewedge and receiving hole make up an engageable collet-type anchorage.This is the preferred type of anchorage with which the present inventionis to be used. However, any type of anchorage which is engageableresponsive to the application of lateral force thereto could be used.

The use of such a collet device has certain inherent problems. If thecollet is designed to be self-actuating, that is to engage itself to thetendon as the externally applied tension is released and it begins toshrink back to its normal length, there will be a tension lossassociated with the amount of tendon shrinkage necessary to effectivelyengage the collet to the tendon and to seat the collet against theabutting portion of the structure. The amount of tension loss associatedwith a given amount of shrinkage will vary depending upon thelength,cross section and modulus of elasticity of the particular tendoninvolved. Also, the process of initially overtensioning the tendon toovercome frictional effects is made more difficult because the colletmust be restrained from self-engagement during the tension reductionstage.

If the collet is forcibly engaged by manual means such as hammering, theprocess becomes prohibitively slow. This is especially undesirable withthe use of a multiple stranded tendon which requires engagement of eachstrand separately. The use of a hydraulically actuated piston used toengage and seat or locl the collet as disclosed in U.S. Pat. No.3,090,598 remedies this problem by providing a locking piston" for thepositive engagement of the engageable collet. But this has its ownshortcomings inasmuch as the time involved in setting up the anchorageelements and the locking piston decreases the efficiency with which theexpensive multifunction hydraulic jack suggested therein is utilized.

SUMMARY OF THE INVENTION The present invention seeks to remedy these andother shortcomings in the prior art by providing for the use of twocoaxially located, but separable, jacks. When positioned over one end ofa tendon, they cooperate to stress and anchor that tendon to thestructure. Their separable character is intended to facilitate moreefficient implementation of the most expensive piece of equipment, thepulling jack, by allowing a staged assembly. With the use of thisinvention, a plurality of setup The foregoing abstract summarizes themethod and ap paratus of the invention. A more precise definition isfound in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of theposttensioning apparatus assembled and ready for operation, with theextended position of the pulling jack shown in phantom. FIG. 2 is anexploded view of the apparatus.

FIG. 3 is a'longitudinal sectional view of the anchoring collet, theengaging jack and a pulling vise assembled upon strands of aprestressing tendon, with the pulling jack shown in phantom.

FIG. '4 isa sectional view of the collet anchor the engaging jack andthe pulling jack attached to the pulling vise, with the pulling jack inits extended condition as it imparts tension to the strands of aprestressing tendon. 4

FIG. 5 is a detailed sectional view of the engaging jack as it engagesthe engageable collet anchor.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now in detail to thedrawings, a concrete structure in the form of a beam or column isdesignated therein by the numeral 10. The structure is typical of thetype used for posttensioning processes and includes a multistrandprestressing tendon 12 extending longitudinally therethrough. One end ofthe tendon, as can be seen in the drawings, protrudes from thestructure. While not illustrated, it should be understood that the otherend of the tendon would be suitably anchored to the structure and,possibly, protrude therefrom.

STRUCTURE AND ASSEMBLY Prior to the process of posttensioning theprestressing tendon 12, the elements making up the apparatus areassembled around the end of the tendon extending from the structure. Inthe following discussion, these elements will be described in thesequence in which they are assembled into place.

The first of the elements comprises a bearing plate 14 having an opening16 extending through the central portion thereof. The plate I4 is seatedagainst the end of the structure I0 with the strands of the tendon 12extending through the opening 16. For convenient reference the strandsare designated 12a.

The next of the elements comprises an engageable collet anchor 18threaded over the strands of the tendon 12 in abutting engagement withthe plate 14. The anchor 18 is of the type conventionally employed foranchoring prestressing tendons in place and comprises a plate 20 havinga plurality of conical apertures 22 extending therethrough, and a pairof collar-shaped wedges 24 loosely received in each of the aper tures.The anchor 18 is assembled into place so that the apertures 22 convergetowards the plate 14. Each strand 12a making up the tendon, I2 extendsthrough one of the apertures 22 and is surrounded by a pair of thewedges 24.. The strands 12a. plate 20 and wedges 24 are so interrelatedthat, upon forcing of the wedges into the apertures 22, the wedgessimultaneously seat in the apertures 22 and assume gripping engagementwith the strands. It is through this operation that the strands are,ultimately, anchored.

Adjacent the collet anchor 18, a seating plate 26 is threaded over thestrands of the tendon 12 and disposed for movement toward andsimultaneous abutting engagement with the wedges 24 of the collet anchor18. The seating plate 26 is peripherally threaded and has a plurality ofapertures 28 extending therethrough, each of which is of a sizesufficient to closely, but slidably, receive one of the tendon strands12a. They are arranged in a'pattern corresponding to those in the anchor18. Thus, when the plate 26 is assembled into place with each strand1211 making up the tendon 12 extending through an aperture 28, movementof the plate 26 toward the anchor 18 will bring the plate 26 intoabutment with the wedges 24 protruding from the anchor plate 20 of theanchor 18.

An engaging jack 30 is received over the tendon 12 to one side of theplate 26. lt is of relatively conventional center hole type constructionand comprises a hollow inner member 30a and a hollow outer member 301;selectively expansible relative to each other. The inner expansiblemember 30a is disposed toward the structure and is internally threadedto receive the seating plate 26 therein. The tendon 12 extends throughthe hollow center 32. A face 34 on the outer member 30b is formed tocooperatively abut with structure within a pulling jack 36, which willbe described in detail later, to restrain the motion of the engagingjack 30 away from the structure 10. Thus disposed and restrained,expansion of engaging jack 30 will move the seating plate 26 intoabutment with the wedges 24 of the anchor 18. The lateral force soapplied to the anchor 18 will bring the anchor plate 20 into bearinginterrelationship with the structure and effect gripping engagement ofthe tendon 12 by forcing the wedges 24 into the conical apertures 22.

A pulling vise 38, identical in structure and operation to the collctanchor 18 is assembled over the tendon to one side of the plate 26. Itcomprises a vise plate 40 having a conical apertures 36 convergingtoward the structure and collar-shaped wedges 42 received in theapertures. As assembled, it is received over the tendon 12 adjacent theengaging jack 30 and grippingly engaged to the tendon strands [2a.

A center hole hydraulic pulling jack 46 having a hollow inner member 460and a hollow outer member 46b selectively expansible relative to eachother is positioned over the abovedescribed assemblage with the outermember 46b disposed toward the structure 10. At the end of the pullingjack 46 nearest the structure 10, the walls of the outer member 4611form a housing 48 adapted to pass over and receive the engaging jack 30,the seating plate 26 and the engageablc collct anchor 18 when the distalend of the outer member 46); abuts the bearing plate 14. Slots 49 extendlaterally through the housing 48 to provide for access to the jack 30and accommodate the connection of hydraulic lines thereto. The housing48 is of increased diameter relative to the cylindrically hollow center,designated 50, of the member 46b. The transition between the twodiameters is square-cut to form an abutting surface 52 which cooperateswith the face 34 of the outer member of the engagingjack 30b to restrainthe motion ofthat outer member 30!: away from the structure 10 when theouter member 46b of the pullingjack 46 is similarly restrained.

The hollow center 50 of the inner member 460 is formed to receive apulling tube 54. The end of the tube most remote from the structure 10threadably receives a ring nut 56 which is keyed thereto, as seen at 58.The keyed interrelationship is provided to prevent relative rotationbetween the nut 56 and the pulling tube 54, once the nut and tube arethreadably engaged by means of threaded portions, designated 60. Theopposite end of the pulling tube 54 is provided with an internallythreaded portion 62 to engage the pulling vise 38. When the pulling jack46 is positioned around the tendon 12 with the above-describedassemblage in place, the pulling tube 54 is slid through the center ofthe pulling jack 50 and is rotated by means of the ring nut 56 until thepulling vise 38 has been engaged and the ring nut 56 abuts the outwardend of the inner member of the pullingjack 4611.

Hydraulic lines 64 and 66 are attached to the jacks 30 and 46,respectively, to effect the operation thereof during the posttensioningoperation.

OPERATION By selectively connecting the hydraulic lines 64 and 66 to asource of hydraulic pressure, not shown, the expansible members of thejacks 46 and 30 may be expanded or collapsed as required by theposttensioning procedure. This procedure comprises tensioning the tendon12 by expanding the pulling jack 46, and then partially relaxing thattension to achieve a uniform stress distribution along the tendon 12.While the relaxing step may be omitted, it is generally preferred foroptimum results. With the pulling jack 46 now in tensioned engagementwith the tendon, and the outer member 46!; thus restrained from movementaway from the structure l0, the engagingjack 30, which rests in abutmentupon the abutting surface 52, is expanded to cause the seating plate 26to abut the collar-shaped wedges 24, seat the anchor plate 20 firmlyagainst the bearing plate 14 and wedge the collar-shaped wedges 24between the tendon strands 12a and the sloping sides of the conicalapertures 22 in the anchor plate 20. With the tendon 12 so anchored tothe structure l0, both jacks 30 and 46 are then collapsed. Once thusconditioned, the pulling jack 46 may be counterrotating the ring nut 56,thus disengaging the pulling tube 54 from the pulling vise 38. Thepulling tube 54 is then removed from the pulling jack 46, allowing thepulling jack 46 to be removed from around the inner asscmblage and to betaken to another location for similar use. Finally, the pulling vise 38,engaging jack 30 and seating plate 26 may be removed to be used inanother location.

METHOD From the foregoing description, the method ofthe invention isbelieved apparent. First the elements are sequentially assembled intoplace. Once assembled, the elements are operated to selectively tensionthe tendon and anchor it in place. In the latter operation, the tendon12 may be partially relaxed prior to anchorage to equalize the tensiontherein. Once the anchor 18 is set, the engaging jack 30 is relaxed andthen the pulling jack 46 is relaxed. The method is completed by removingthe jacks 46 and 30 and seating plate 26 to leave the tendon l2 anchoredin place by the engagcablc anchor structure [8.

CONCLUSlON While but a single tensioning operation has been described,it should be understood that the apparatus and method of the inventionare ideally suited to multiple tensioning operations wherein it isnecessary to tension tendons located at a plurality oflocations. In suchan environment, a single pullingjack may be used with a plurality ofengaging jacks and anchorage assemblies. In this way, engagingjack andanchorage assemblies may be set up at one location while the pullingjack is being used at another location and, thus, the pulling jack maybe maintained in substantially continuous use. The fact that the pullingjack may be assembled over an engaging jack after it has beenpreassembled into place and removed while the engagingjack is still inplace optimizes this operation.

The use of the term strand as herein employed is intended to applyequally to a strand comprised of a single wirelike ele ment, as well asa strand comprised of a plurality of tightly grouped small-wire likeelements.

lclaim:

1. An assemblage for applying tension to and anchoring the end of aprestressing tendon extending from a concrete structure, said assemblagecomprising:

a. anchoring means disposed around said tendon for seating engagementwith said structure and selective gripping en gagement of said tendonupon the application of compressive force to said means;

b. a first jack having a base member disposed in compression impartingrelationship to said structure and a ram selectively expansible relativeto said base member disposed in gripping engagement with said tendon;and

c. a separable second jack releasably connected to said first jack, saidsecond jack having a base member restrained against movement away fromsaid structure by said first jack base member and a ram selectivelyexpansible relative to said second jack base member and disposed formovement towards and into abutting engagement with said anchoring means7 to impart compressive force thereto to effect gripping said tendon andseating said anchoring means against said structure.

2. The assemblage as described in claim 1 wherein the anchoring meanscomprises:

a. an anchoring plate in abutting engagement with said second jack basemember and having a truncated conical hole through which the tendon isdirected; and,

b. internally toothed collar-shaped wedges received around the tendon,said wedges being adapted, under the application of compressive forcethereto by said second jack ram upon expansion thereof relative to saidsecond jack base member, to wedge into the anchor plate hole andgrippingly engage said tendon,

3. The assemblage as described in claim 2 wherein:

a. the second jack base member defines a cavity;

b. the tendon is comprised of a plurality of strands;

c. the anchoring plate is at least partially disposed within said cavityand in abutting engagement with the wall of said second jack base memberdefining said cavity, said anchoring plate having at least one suchtruncated conical hole for each strand of said tendon, said holes.disposed in a uniform pattern across said plate; and,

d. toothed collar-shaped wedges are provided for each strand togrippingly engage each strand responsive to a common compressive forceapplied thereto.

4. An assemblage for applying tension to and anchoring the end of aprestressing tendon extending from a concrete structure, said assemblagecomprising:

a. anchoring means disposed around said tendon for seatin engagementwith said structure and selective gripping engagement of said tendonupon the application of compressive force to said means;

b. a first jack having a base member disposed in compression-impartingrelationship to said structure and a ram selectively expansible relativeto said base member disposed in gripping engagement with said tendon;and

c. a second jack interposed between said first jack and said anchoringmeans, said second jack having a base member restrained against movementaway from said structure and a ram selectively expansible relative tosaid base member and disposed for movement towards and into abuttingengagement with saidanchoring means to impart compressive force theretoto effect gripping said tendon and seating said anchoring means againstsaid structure;

said first jack being of the center hole type and formed with a cavitywithin the base member thereof to receive said anchoring means and saidsecond jack and said second jack being restrained from movement awayfrom the structure by an abutting engagement between the base member ofsaid second jack and a wall of the cavity in the a base member of saidfirst jack.

5. A center hole pulling jack for use in imparting tension to a tendonextending from a concrete structure, said jack comprising:

a. a base member adapted to be seated against the structure,

said base member having:

1. a cavity in and opening through the distal end thereof of a sizesufficient to freely pass over and receive an independent expansiblecenter hole jack;

2. a surface within said cavity and spaced from the open end thereofagainst which an independent jack received therein may bear whereby,upon expansion, movement of said independent jack away from a structureagainst which said base member is seated is restrained;

3. an open area within said cavity and communicating with the open endthereof through which an independent jack received thereinmay expand;and,

i 4'. an elongated throughbore formed in said base member andcommunicating with said cavity, said surface surrounding saidthroughbore; and

b. a ram expansible relatiye to said base member. 6. The ack asdescribed In claim 5 wherein, an opening extends laterally through saidbase member and into communication with the cavity therein to permitaccess to an independent jack received in said cavity.

7. A method of posttensioning and anchoring the end of a prestressingtendon extending from a concrete structure by means of an engageablecollet which grips said tendon responsive to application of acompressive force thereto and anchors the tendon to the structure,comprising:

a. positioning the engageable collet adjacent said structure and aroundthe emerging end of the prestressing tendon;

b. positioning an engaging jack having two portions selectivelyexpansible relative to each other to restrain one of said portionsagainst movement away from said structure and dispose the other forselective movement toward and into abutment with said engageable colletto effect the gripping engagement of said collet with said tendon andforce said collet into bearing interrelationship with said structure;

c. positioning around the tendon, the engaging jack and engageablecollet, a center hole pulling jack having two hollow portionsselectively expansible relative to each other, with one portiondisposed'in compression imparting relationship to said structure, andthe other portion disposed in gripping engagement to the end of saidtendon;

d. expanding'said pulling jack to impart a predetermined tension to saidtendon;

e. expanding said engaging jack to force the collet into grippingengagement with the tendon and bearing inter relationship with thestructure; f. collapsing the engaging jack;

g. collapsing the pulling jack;

h. removing the pulling jack; and

i. removing the engaging jack.

8. The method as described in claim 7, wherein:

a. prior to engaging the engageable'collet, the pulling jack is expandedto impart a tension in excess of the predetermined amount ultimatelydesired to overcome frictional effects along the length of the tendon;

b. the pulling jack is partially collapsed to impart a uniformpredetermined tension to the tendon; and,

c. the engaging jack is then expanded to engage the engageable collet.

9. The method as described in claim 7, wherein:

a. the tendon is composed of a plurality of strands;

b. the engageable collet is of the type adapted to individuallyaccommodate a plurality of strands and is positioned so that each strandof the tendon is individually surrounded thereby;

c. a single pulling jack is employed to simultaneously engage andtension all of the strands; and,

d. a single engaging jack is employed to simultaneously engage thecollet to all of the strands;

e. the one portion of said engaging jack is restrained against movementaway from the structure by abutment with said pulling jack.

10. The method as described in claim 9, wherein:

a. prior to engaging the engageable collet, the pulling jack is expandedto impart a tension in excess of the predetermined amount ultimatelydesired to overcome frictional effects along the length of the tendon;

b. the pulling jack is partially collapsed to impart a uniformpredetermined tension to the tendon; and,

c. the engaging jack is then expanded to engage the engageable collet.

c. the engaging jack is then expanded to engage the engageable collet.

1. An assemblage for applying tension to and anchoring the end of aprestressing tendon extending from a concrete structure, said assemblagecomprising: a. anchoring means disposed around said tendon for seatingengagement with said structure and selective gripping engagement of saidtendon upon the application of compressive force to said means; b. afirst jack having a base member disposed in compression impartingrelationship to said structure and a ram selectively expansible relativeto said base member disposed in gripping engagement with said tendon;and c. a separable second jack releasably connected to said first jack,said second jack having a base member restrained against movement awayfrom said structure by said first jack base member and a ram selectivelyexpansible relative to said second jack base member and disposed formovement towards and into abutting engagement with said anchoring meansto impart compressive force thereto to effect gripping said tendon andseating said anchoring means against said structure.
 2. The assemblageas described in claim 1 wherein the anchoring means comprises: a. ananchoring plate in abutting engagement with said second jack base memberand having a truncated conical hole through which the tendon isdirected; and, b. internally toothed collar-shaped wedges receivedaround the tendon, said wedges being adapted, under the application ofcompressive force thereto by said second jack ram upon expansion thereofrelative to said second jack base member, to wedge into the anchor platehole and grippingly engage said tendon.
 2. a surface within said cavityand spaced from the open end thereof against which an independent jackreceived therein may bear whereby, upon expansion, movement of saidindependent jack away from a structure against which said base member isseated is restrained;
 3. The assemblage as described in claim 2 wherein:a. the second jack base member defines a cavity; b. the tendon iscomprised of a plurality of strands; c. the anchoring plate is at leastpartially disposed within said cavity and in abutting engagement withthe wall of said second jack base member defining said cavity, saidanchoring plate having at least one such truncated conical hole for eachstrand of said tendon, said holes disposed in a uniform pattern acrosssaid plate; and, d. toothed collar-shaped wedges are provided for eachstrand to grippingly engage each strand responsive to a commoncompressive force applied thereto.
 3. an open area within said cavityand communicating with the open end thereof through which an independentjack received therein may expand; and,
 4. An assemblage for applyingtension to and anchoring the end of a prestressing tendon extending froma concrete structure, said assemblage comprising: a. anchoring meansdisposed around said tendon for seating engagement with said structureand selective gripping engagement of said tendon upon the application ofcompressive force to said means; b. a first jack having a base memberdisposed in compression-imparting relationship to said structure and aram selectively expansible relative to said base member disposed ingripping engagement with said tendon; and c. a second jack interposedbetween said first jack and said anchoring means, said second jackhaving a base member restrained against movement away from saidstructure and a ram selectively expansible relative to said base memberand disposed for movement towards and into abutting engagement with saidanchoring means to impart compressive force thereto to effect grippingsaid tendon and seating said anchoring means against said structure;said first jack being of the center hole type and formed with a cavitywithin the base member thereof to receive said anchoring means and saidsecond jack and said second jack being restrained from movement awayfrom the structure by an abutting engagement between the base member ofsaid second jack and a wall of the cavity in the base member of saidfirst jack.
 4. an elongated throughbore formed in said base member andcommunicating with said cavity, said surface surrounding saidthroughbore; and b. a ram expansible relative to said base member.
 5. Acenter hole pulling jack for use in imparting tension to a tendonextending from a concrete structure, said jack coMprising: a. a basemember adapted to be seated against the structure, said base memberhaving:
 6. The jack as described in claim 5 wherein, an opening extendslaterally through said base member and into communication with thecavity therein to permit access to an independent jack received in saidcavity.
 7. A method of posttensioning and anchoring the end of aprestressing tendon extending from a concrete structure by means of anengageable collet which grips said tendon responsive to application of acompressive force thereto and anchors the tendon to the structure,comprising: a. positioning the engageable collet adjacent said structureand around the emerging end of the prestressing tendon; b. positioningan engaging jack having two portions selectively expansible relative toeach other to restrain one of said portions against movement away fromsaid structure and dispose the other for selective movement toward andinto abutment with said engageable collet to effect the grippingengagement of said collet with said tendon and force said collet intobearing interrelationship with said structure; c. positioning around thetendon, the engaging jack and engageable collet, a center hole pullingjack having two hollow portions selectively expansible relative to eachother, with one portion disposed in compression imparting relationshipto said structure, and the other portion disposed in gripping engagementto the end of said tendon; d. expanding said pulling jack to impart apredetermined tension to said tendon; e. expanding said engaging jack toforce the collet into gripping engagement with the tendon and bearinginterrelationship with the structure; f. collapsing the engaging jack;g. collapsing the pulling jack; h. removing the pulling jack; and i.removing the engaging jack.
 8. The method as described in claim 7,wherein: a. prior to engaging the engageable collet, the pulling jack isexpanded to impart a tension in excess of the predetermined amountultimately desired to overcome frictional effects along the length ofthe tendon; b. the pulling jack is partially collapsed to impart auniform predetermined tension to the tendon; and, c. the engaging jackis then expanded to engage the engageable collet.
 9. The method asdescribed in claim 7, wherein: a. the tendon is composed of a pluralityof strands; b. the engageable collet is of the type adapted toindividually accommodate a plurality of strands and is positioned sothat each strand of the tendon is individually surrounded thereby; c. asingle pulling jack is employed to simultaneously engage and tension allof the strands; and, d. a single engaging jack is employed tosimultaneously engage the collet to all of the strands; e. the oneportion of said engaging jack is restrained against movement away fromthe structure by abutment with said pulling jack.
 10. The method asdescribed in claim 9, wherein: a. prior to engaging the engageablecollet, the pulling jack is expanded to impart a tension in excess ofthe predetermined amount ultimately desired to overcome frictionaleffects along the length of the tendon; b. the pulling jack is partiallycollapsed to impart a uniform predetermined tension to the tendon; and,c. the engaging jack is then expanded to engage the engageable collet.